A thin semiconductor device which has a smaller thickness than the existing semiconductor device has been developed in order to improve the performance of a semiconductor device made of, for example, silicon (Si), silicon carbide (SiC), or gallium nitride (GaN). When the thin semiconductor device is manufactured, for example, a front surface element structure and a front surface electrode are formed on the front surface side of a wafer, the rear surface of the wafer is ground to a desired thickness (the wafer is thinned), and a rear surface element structure is formed on the ground rear surface of the wafer.
In recent years, as a technique for reducing the thickness of the wafer, the following processes have been known: a TAIKO (registered trademark) process which leaves an outer circumferential portion of the wafer as a reinforcing portion (rib portion) and mechanically grinds only a central portion of the wafer to reduce the thickness of the wafer; and a wafer support system (WSS) process that reinforces a wafer with a supporting substrate and reduces the thickness of the entire wafer. In the TAIKO process, the outer circumferential portion of the wafer remains with the original thickness, without being ground. Therefore, mechanical strength is ensured and the breaking or warping of the wafer is reduced. However, the TAIKO process has a limitation in manufacturing an ultrathin device with a thickness of, for example, 50 μm or less.
As a method for solving the above-mentioned problems, in recent years, a technique for forming a thin device using the WSS process has been developed. In the WSS process, a supporting substrate is bonded to a wafer by an adhesive to ensure the mechanical strength of the wafer. Therefore, it is possible to reduce the thickness of the wafer. The material forming the adhesive is determined by resistance to a manufacturing process or a method for peeling the supporting substrate from the wafer. In general, a method for breaking the chemical bond between the supporting substrate and the adhesive using laser irradiation is used in order to peel the supporting substrate from the wafer. In addition, there is a method which dissolves the adhesive with a solvent or softens the adhesive with heat to reduce the adhesion between the adhesive and the supporting substrate.
Next, a method for manufacturing a thin device using the WSS process according to the related art will be described. FIGS. 17 to 21 are cross-sectional views illustrating the state of a semiconductor device according to the related art during manufacture. First, front-surface-side processing is performed on a wafer 101 to form a front surface element structure (not illustrated) on the front surface side of the wafer 101. Then, an adhesive is applied onto the entire front surface of the wafer 101 by a coater and is then cured to form an adhesive layer 102. Then, a glass substrate 103 is bonded to the front surface of the wafer 101 on which the adhesive layer 102 is formed. This state is illustrated in FIG. 17. Then, the wafer 101 is turned so that the rear surface of the wafer 101 is up. Then, the rear surface of the wafer 101 is ground to reduce the thickness of the wafer 101.
Then, rear-surface-side processing is performed on the wafer 101 to form a rear surface element structure (not illustrated) on the rear surface of the wafer 101. This state is illustrated in FIG. 18. Then, the wafer 101 is turned so that the rear surface of the wafer 101 is down and is then bonded to a dicing tape 112 fixed by a dicing frame 111 (FIG. 19). Then, a laser beam 113 is radiated to the glass substrate 103 to break the chemical bond between the glass substrate 103 and the adhesive layer 102 (FIG. 20). Then, the glass substrate 103 is peeled from the front surface of the wafer 101 and the adhesive layer 102 is removed by, for example, a solvent. Then, the wafer 101 is cut into individual chips 104 by a dicing blade 114. In this way, the chip 104 having a thin semiconductor device formed thereon is completed (FIG. 21).
As a method for peeling the supporting substrate bonded to the wafer, the following method has been proposed: a separation method which separates a supported substrate from a support in a laminate including a light-transmissive support, the supported substrate which is supported by the support, an adhesive layer provided on a surface of the supported substrate which is supported by the support, and a separation layer which is provided between the support and the supported substrate and is made of fluorocarbon. In the method, light is radiated to the separation layer through the support to change the properties of the separation layer (for example, see the following Patent Document 1).
As another method, the following method has been proposed: a separation method which separates a supported substrate from a support in a laminate including a light-transmissive support, the supported substrate which is supported by the support, an adhesive layer provided on a surface of the supported substrate which is supported by the support, and a separation layer which is provided between the support and the supported substrate and is made of an inorganic material. In the method, light is radiated to the separation layer through the support to change the properties of the separation layer (for example, see the following Patent Document 2).
As still another method, the following method has been proposed: a laminate separation method which separates a support from a substrate in a laminate including an infrared-transmissive support, a supported substrate which is supported by the support, an adhesive layer which bonds the supported substrate and the support, and a separation layer that is provided on a surface of the support, to which the supported substrate is bonded, and is made of a compound having an infrared absorbing structure. In the method, infrared rays are radiated to the separation layer through the support to change the properties of the compound (for example, see the following Patent Document 3).